Field of the Invention
An e-bike or a pedelec (“pedal electric cycle”) is an electric bicycle, where the rider's pedaling is assisted by an electric motor. Typically, a torque exerted on the pedal or the bottom bracket is measured and the electric motor supports the mechanic driving power in accordance with the exerted torque. For example, the support may be the larger, the larger the force exerted by the rider is. For measuring the exerted torque magneto elastic torque sensors are used, which are built in the bottom bracket and which measure a change of the magnetic field due to the magneto elastic effect. In addition to the change of the magnetic field caused by the torque, the magnetic field sensor measures external noise fields. These external noise fields may be caused by magnetic or magnetized items in the vicinity of the bottom bracket and further by the Earth's magnetic field.
External magnetic fields may lead to a torque that is greater than the real torque being measured so that a false target value is determined for the support or the power to be delivered by the electric motor. For example, in particular during a slow ride or when braking, external magnetic fields may result in an unwanted and surprising strong acceleration which may be dangerous in certain situations such as turning into a main road or at downward slopes on hills and others.